Today, 4-line CCD sensors are commercially available and are commonly used. The 4-line CCD sensor comprise a monochromic reading sensor in which no color filters are arranged on a light receiving surface of a photodiode array in order to read monochromic originals, and a color reading 3-line sensor in which color filters for red, green, and blue (hereinafter referred to as R, G, and B), i.e. the three primary colors, are arranged on the light receiving surfaces of the respective photodiode arrays composed of the same material, in order to read a color original, the monochromic reading line sensor and the color reading 3-line sensor being constituted by the same chip.
The structure of the CCD line sensor is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-76361. Driving of the CCD sensor is disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 11-220569 and 2000-69254.
In this case, sensitivity, an electric characteristic of the CCD line sensor is defined by output power [V/lx. sec] with respect to the quantity of incident light per unit time. Thus, with a 4-line CCD sensor composed of a plurality of CCD sensors, even if the CCD sensors, i.e. the photodiode arrays are irradiated with uniform light energy, i.e. the same quantity of light over the same period, the amplitudes of output signals from the CCD sensors vary according to the transmittal wavelength through the color filters arranged on the light receiving surfaces.
In view of these points, an image input apparatus according to the prior art matches the amplitudes of output signals from the CCD sensors to one another by adjusting the spectral characteristic of a light source according to the sensitivities of a plurality of CCD sensors. Further, if the output signals from the CCD sensors have different amplitudes, the amplitudes of the output signals are matched to one another by adjusting, according to the amplitudes of the output signals, the amplification factor of an amplifier succeeding the CCC sensors, e.g. a gain amplifier composed of an operational amplifier or the like.
On the other hand, with a scanner section as an image input apparatus used for recent color readable digital copiers and digital composite machines, the succeeding circuit carries out adjustment even with the use of a light source having its spectral characteristics limited to some degree.